The present case is generally directed to detecting a fixed mechanical reference. Servo data are often used in a control system to provide feedback positional control for a control object. In the environment of a data storage device, such data can be used to detect and control the position of a read/write transducer adjacent a rotatable storage medium.
The servo data can be provided in a number of ways. In one approach, a servo track writer engages a data storage device to write an initial set of servo data to the storage media mounted therein. The initial servo data can take a number of forms, such as a series of spaced apart, continuous spirals that extend across the media surfaces in helical fashion from an outermost diameter (OD) to an innermost diameter (ID). Final servo data are thereafter written using the initial servo data as a prewritten positional reference.